The present invention relates to a radio network system, in which a plurality of radio communication control equipments respectively having communication function with a plurality of radio terminals and connected with each other via a radio main line.
In the recent years, according to advancement of radio communication technology, it has been frequently established a radio communication network for data transmission between terminals since it does not require engineering work for cable connection associated with modification of layout in an office, a store, a factory or the like. However, in order to perform communication in wide area, a main line of the network is constructed as a wired network with an optical fiber, coaxial cable or so forth so as to provide sufficient reliability. Such wired main line is connected to a communication control apparatus. Then, a plurality of radio communication terminals are typically connected to the communication control apparatus in tree connection, bus connection, star connection. As such type of network, it has been known a BREEZNET PROSeries of BREEZECOM Ltd.
It has been desired to form the main line of the network as radio communication line for reducing cabling cost, maintenance cost and so forth. However, when radio network is employed as main line, zones where retransmission process is frequently required for interference of reflected radio wave from ceiling, wall or so forth, environmental noise or so forth, to cause significant fluctuation of transmission rate between communication zones.
When a condition where transmission rate is significantly differentiated between communication zones, occurs, non-processed data may be accumulated in a transmission and reception buffer for relaying of the radio communication control unit of the zone where the transmission rate is lowered. Finally, significant delay of transmission or packet loss is caused to cause interruption of service of the network.
The present invention has been worked out in view of the problem in the prior art as set forth above. It is, therefore, an object of the present invention to prevent occurrence of significant difference of transmission rate between communication zones, and whereby to maintain the transmission rate of overall network constant.
According to one aspect of the present invention, a radio network system, in which a plurality of radio communication control units are connected with each other via radio main line, and each radio communication control unit has a communication function with at least one radio communication terminal arranged within own communication area, each of the radio communication control units comprises:
means for broadcasting a transmission rate restriction demand to all of other radio communication control units and all of radio communication terminals when data amount stored in a transmission and reception buffer exceeds a predetermined threshold value; and
means for lowering a transmission rate when a transmission rate restriction demand is received from any other radio communication control unit within a predetermined period and for increasing the transmission rate when no transmission rate restriction demand is received from any other radio communication control unit.
By this, the transmission rate can be maintained uniform over the entire radio network to prevent occurrence of packet loss and to improve throughput.
In the preferred construction, each of the radio communication control units and the radio communication terminal may modify a time interval of reading the transmission and reception buffer for increasing and decreasing the transmission rate.
By this, data transmission rate can be varied simply without requiring complicate control, such as that varying transmission pulse width.